Method of coating ferrous articles



Dec, 8, 1942. M. M. RUBIN 2,304,709

' METHOD OF COATING FERROUS ARTICLES Filed Oct. 51., 1940 Patentecl Dec. 8, 1942 METHOD OF COATING FERROUS ARTICLES Michael M. Rubin, Warren, Ohio, assignor to The Thomas Steel Company Application October 31, 1940, Serial No. 363,713

1 Claim.

This invention relates, as indicated, to methods of coating ferrous articles, but has reference more particularly to the production of a coppertinalloy coating on such ferrous articles as wire and strip. I

It has heretofore been proposed to form such coatings on ferrous articles of electrodeposition on the articles of the alloy, or by immersing the articles to be coated in a molten bath of the alloy. These methods have generally proved unsatisfactory, as they do not result in the production of a coating of uniform thickness and homogeneity or one that adheres to the base metal with sufllcient tenacity to render the article capable of being subjectedto bending and other fabricating operations.

It is an object of the present invention, accordingly, to provide a method or methods whereby ferrous articles, such as wire and strip, are coated with a uniform, closely adherent coating of a copper-tin alloy.

A further object of the invention is to provide a method of coating which may be continuous in character, whereby production of the alloycoated articles in desired commercial quantities is made feasible, or may, if desired, consist of separate, discontinuous steps or operations.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the steps hereinafter described and particularly pointed out in the claim; the annexed drawing and the following description setting forth in detail one approved method of carrying out the invention continuously, such disclosed steps illustrating, however, but one of the various ways in which the principle of the invention may be used.

The method, broadly stated, consists in sepa-.

rately electrodepositing on the ferrous article, such as a strip or wire, the metals forming the alloy coating, and subsequently heating the coated article, preferably in a controlled atmosphere free from oxidizing gases, to cause an alloying of the electrodeposited metals. In cases where the ferrous article isin an unannealed condition, the heating may be governed or controlled in such a manner, particularly as regards the temperature and time period as to effect an annealing or tempering of the ferrous base metal as well as the alloying of the electrodeposited metals.

The method may be practiced commercially by means of the apparatus shown in the accompanying drawing.

Referring to said drawing, the strip S is drawn cessively through an alkali cleaning tank 2, a rinse tank 3, an acid pickling tank 4, another rinse tank 5, a copper plating tank 6, a rinse say, without first depositing on the ferrous metal a thin layer of metal such as nickel or cobalt, required in some metal coating processes to prevent peeling of superimposed coatings.

The amount of tin which is electrodeposited on the copper may be varied in accordance with the properties which are desired in the alloy from a coil mounted on reel I, and is passed succoating. For the production of commercial bronze coatings, the respective plated coatings will be of such thickness that the amount of copper in the bronze will be in excess of about of the weight of the coating. In other words, the proportion of tin will not exceed 20%:

of the weight of the coating.

The period of time of heating in the chamber l2 will depend upon the thickness of the separate coatings of copper and tin, the thickness or gauge of the base metal or ferrous strip, and the specific temperatures employed. In general, where the base metal is already in the annealed state, a temperature range of from about 400 F. to about 1000 F. is sufllcient to produce an alloying of the coatings, the precise temperature depending upon the speed of the strip through the heating chamber. In cases where the ferrous base metal is in an unannealed condition,and it is desired to anneal the metal and at the same time to obtain an alloying of the coatings, it is necessary to heat the strip to an annealing temperature, which will depend, of course, on the analysis of the base metal, but which, in general, varies from about 1000 F. to about 2000 F. Even where the base metal is in an. annealed condition, it may be desirable to heat at a temperature in excess of 1000 F. to secure an alloying of the coatings, and it is to be understood, therefore, that a heating temperature of from about 400 F. to about 2000 F. may be employed in such cases.

The terms annealing and annealed are here used in their broadest sense, that is, to cover a heating and cooling operation in the solid state,

usually implying a slow cooling, and including such specialized heat treatments as normalizing (see pages 252-254 of the National Metals Handbook, 1933 edition, published by American Society low carbon steel base metal of .015" thickness to be obtained, in a case where the heating chamber l2 was approximately 26 feet long, the amount of copper, .1 oz. per sq. ft. of base metal surface. (.000135" thick), the amount of tin, .025 oz. per sq. ft. of base metal surface, (.00004" thick) and the temperature of the strip 1450 F-.. the strip was passed through the heating chamber in approximately two minutes. Under the same conditions, strip of .030" thickness required three minutes in the heating chamber. The alloy strip, upon emerging from the heating chamber I 2, is cooled in the cooling chamber lit at such a rate as will produce a desired annealing or tempering of the base metal.

The atmosphere within the furnace II is a controlled non-oxiding or reducing atmosphere, provided by the use of "DX or other gas prepared by the partial combustion of natural gas. DX is a gas consisting of 80% nitrogen, 5-6% hydrogen, 7-9% carbon dioxide and 7-9% carbon monoxide. Such a protective gas is instrumental in inhibiting oxidation of the electrodeposited metals or the bronze alloy, especially at the higher temperatures employed,

The alloy coating, thus formed, is of uniform thickness, homogeneous in character, and adheres to the ferrous base metal with a tenacity suflicient to render the coated metal capable of being subjected to bending and various other operations employed in fabricating articles from such coated metal.

In cases where, due tolimitations in the length of the building in which the apparatus is to be installed, the apparatus cannot be arranged in a single line, as diagrammatically illustrated in the drawing, the strip S, after emergence from the drying oven l0, may be coiled up and the strip, as unwound from such coil, then run through the furnace II which may be in another part of the building.

Instead of heating the coated strip in a continuous type furnace of the character described, the strip, after emergence from the drying oven l0, may be coiled up, and the coils or a plurality of such coils of strip may be placed in an annealing box or an electrically heated bell-type furnace and heated in such box or furnace at a suitable temperature and for a period of time sufiicient to produce the desired alloying of the coating metals, after which the coils are slowlycooled to atmosphere temperatures. In general, where the base metal is already in the annealed state, a temperature range of from about 400 F. to about 1000 F., and a period of heating of from about 1 to 20 hours, depending upon the relative proportions and thickness of the copper and tin, are suflicient to produce an alloying of the coatings. Where the base metal is to be annealed, a temperature of from about 1000 F. to about 2000 F., and a period of heating of from about 1 to about 20 hours, and slow cooling to atmospheric temperatures, are sufllcient to obtain an alloying of the coatings and an annealing oi the base metal.

To obtain an alloying of the coatings and at the same timeenable a dead soft temper of a low carbon steel base metal to be obtained, the coils after being placed in the annealing box, were heated to about 1300 F. for from about 1 to 4 hours, then permitted to cool gradually to about 250 F.

When the coils are placed in an annealing box, the furnace in which such box is placed should be capable of bringing the contents of the box, i. e., the load, to a uniform temperature in a reasonable length of time without overheating any part of the load, and of maintaining such temperature within plus or minus 15 Fahrenheit degrees.

In using a bell-type furnace, similar condition of temperature and time are observed.

Where the coils are heated in an annealing box or a bell-type furnace, the use of a nonoxidizing atmosphere in the box or fumace'is not necessary, but such an atmosphere may be used, if desired.

Because of the ease and accuracy with which the electrode position of the individual metals, copper and tin in this instance, may be controlled, the composition of the alloy coating may be more closely and readily controlled than in the case of the method previously referred to in which an alloy coating is directly deposited on the base metal, Thus, coatings of any of the well-known copper-tin alloys may be obtained by merely varying the thickness of the coating of each of the individual metals, since in this manner any desired ratio of such metals may i be obtained, and it is unnecessary tov change the composition of the plating baths.

This application is a continuation in part of my co-pending application, Serial No. 166,689, filed September 30, 1937, and allowed June 12, 1940.

Other modes of applying-the principle of the invention may be employed instead of the one explained, change being made as regards the methods herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be emplayed.

I therefore particularly point out and distinctiy claim as my invention The method of coating and annealing unannealed ferrous strip which comprises consecutively subjecting the strip to the action of a copper plating bath to form a coating of copper directly thereon, and then to the action of a tin plating bath to form a coating of tin direct- 1y on the copper, heating at a temperature of about 1000 F. to about 2000 F. in a non-oxidizing atmosphere, for a period of time sufllcient to cause an alloying of the copper and tin to form a non-peeling bronze coating, the respective plated coatings being of such thickness that the amount of copper in the bronze will be in excess of about and then cooling the heated strip at such a rate as will produce an annealing of the ferrous strip.

MICHAEL M. RUBIN. 

